Conventional rotary compressors of the above type include one in which refrigerant is compressed by volume change of a cylinder chamber in association with eccentric rotation of an annular piston within an annular cylinder chamber (see for example, Japanese Unexamined Patent Publication No. 6-288358). In the compressor (100), a hermetic casing (110) accommodates a compression mechanism (120) and a motor (not shown) for driving the compression mechanism (120), as shown in FIG. 11 and FIG. 12 (a cross-sectional view taken along the line XII-XII in FIG. 11: not hatched).
The compression mechanism (120) includes a cylinder (121) having an annular cylinder chamber (C1, C2) and an annular piston (122) arranged in the cylinder chamber (C1, C2). The cylinder (121) includes an outer cylinder (124) and an inner cylinder (125) which are arranged coaxially so that the cylinder chamber (C1, C2) is formed between the outer cylinder (124) and the inner cylinder (125).
The cylinder (121) is fixed to the casing (110). Furthermore, the annular piston (122) is coupled through a circular piston base (160) to an eccentric portion (133a) of a drive shaft (133) connected to the motor to eccentrically rotate around the center of the drive shaft (133).
The annular piston (122) eccentrically rotates while keeping substantially in contact at one point of its outer peripheral face with the inner peripheral face of the outer cylinder (124) (wherein “substantially in contact” means a state in which though a minute gap is present to an extent that an oil film is formed, leakage of refrigerant in the gap is ignorable) and substantially in contact, at one point of the inner peripheral face 180° different in phase from the above contact point, with the outer peripheral face of the inner cylinder (125). Thus, an outer cylinder chamber (C1) and an inner cylinder chamber (C2) are formed on the outside and the inside of the annular piston (122), respectively.
An outer blade (123A) is arranged outside the annular piston (122), and an inner blade (123B) is arranged inside the annular piston (123) on an extension line of the outer blade (123A). The outer blade (123A) is forced inward in the radial direction of the annular piston (122) so that the inner peripheral end thereof is pressed against the outer peripheral face of the annular piston (122). The inner blade (123B) is forced outward in the radial direction of the annular piston (122) so that the outer peripheral end thereof is pressed against the inner peripheral face of the annular piston (122).
The outer blade (123A) divides the outer cylinder chamber (C1) into two chambers, and the inner blade (123B) divides the inner cylinder chamber (C2) into two chambers. To be specific, the outer blade (123A) divides the outer cylinder chamber (C1) into a low pressure chamber (C1-Lp) and a high pressure chamber (C1-Hp), and the inner blade (123B) divides the inner cylinder chamber (C2) into a low pressure chamber (C2-Lp) and a high pressure chamber (C2-Hp). Further, in the outer cylinder (124), a suction port (141) for allowing the outer cylinder chamber (C1) to communicate with an suction pipe (114) provided at a casing (110) is formed in the vicinity of the outer blade (123A). Also, in the annular piston (122), a through hole (143) is formed in the vicinity of the suction port (141) so that the low pressure chamber (C1-Lp) of the outer cylinder chamber (C1) and the low pressure chamber (C2-Lp) of the inner cylinder chamber (C2) communicate with each other through the through hole (143). Further, a discharge port (not shown) for allowing the high pressure chambers (C1-Hp, C2-Hp) of the cylinder chambers (C1, C2) to communicate with a high pressure space (S) in the casing (110) is formed in the compression mechanism (120).
In this example, in order to allow only eccentric rotation (orbital motion) while preventing rotation of the annular piston (122) on the axis thereof, an Oldham mechanism (161) is provided as a mechanism for preventing the rotation of the annular piston (122) on the axis thereof.
In the above compression mechanism (120), when the drive shaft (133) rotates to eccentrically rotate the annular piston (122), volume expansion and contraction are repeated alternately in both the outer cylinder chamber (C1) and the inner cylinder chamber (C2). In the volume expansion of each cylinder chamber (C1, C2), a suction process is performed in which refrigerant is sucked into the cylinder chamber (C1, C2) from the suction port (141). Performed in the volume contraction are a compression process in which refrigerant is compressed in the cylinder chamber (C1, C2) and a discharge process in which refrigerant is discharged from the cylinder chamber (C1, C2) to the high pressure space (S) in the casing (110) through the discharge port. Thus, the high-pressure refrigerant discharged into the high pressure space (S) of the casing (110) flows into a condenser of a refrigerant circuit through a discharge pipe (115) provided in the casing (110).
As illustrated in FIG. 13, an example obtained by partly modifying the structure of the rotary compressor illustrated in FIG. 12 is also disclosed in Japanese Unexamined Patent Publication No. 6-288358. In this compression mechanism (120), an annular piston (122) is cut to form a shape of C, and a single blade (123) passes through the cut part of the piston (122) and is thus in contact with the inner peripheral face of the outer cylinder (124) and the outer peripheral face of the inner cylinder (125). A part of the inner peripheral face of the outer cylinder (124) being in contact with the blade (123) is formed to have the same radius of curvature as the outer peripheral face of the inner cylinder (125). Furthermore, an unshown Oldham mechanism is provided to allow eccentric rotation (orbital motion) of the annular piston (122) around the inner cylinder (125) and prevent rotation of the annular piston (122) on the axis thereof. This example is similar to examples illustrated in FIGS. 11 and 12 in that the suction process, compression process and discharge process for refrigerant are performed according to the eccentric rotation of the annular piston (122).